This invention relates to a filtering system and especially to a single filter which can be used in place of the plural contiguous filter channels used in over-the-horizon radar.
Over-the-horizon radar as described in copending U.S. Patent applications Ser. No. 649,791, filed 6/27/67, now U.S. Pat. No. 3,885,240, and Ser. No. 285,555, filed 5/31/63, now U.S. Pat. No. 3,905,034, is used to detect various types of moving objects which impart doppler frequencies to the reflections corresponding to the velocity and acceleration characteristics of the targets. The received signals cover a range of doppler frequencies starting at zero Hz. The system that has been used in the past to detect echoes in this type of radar record the received signal in a storage memory and then to take the stored signals and pass them through sets of paralleled contiguous filters before coupling them to a velocity-and-acceleration analyzer which employs different frequency-swept signals to endeavor to match the frequency characteristics of any echo which has been received. Each parallel filter comprises two bandpass filters, an amplifier and a limiter, and may include a gate. Thus, the filter system employs an enormous amount of hardware.